Rare earth element mobility during laterization of mafic rocks of the Oman ophiolite

Abstract

Eleven samples representing a sequence of progressive alteration through a laterite profile of Upper Cretaceous age developed on a layered gabbro from the Oman ophiolite have been analyzed for their rare earth element (REE) contents. The results provide new insights into the fractionation and vertical movement of REEs during the laterization of mafic parent rocks. Compared to the fresh parent rock, from the same section nearly flat chondrite-normalized REE patterns are observed in the saprolite zone, while light REE (LREEs: La-Nd)-enriched patterns characterize the oxide and clay zones. The altered gabbro shows a depletion in middle REEs (MREEs: Sm-Ho) compared to its unaltered counterpart. A negative cerium (Ce) anomaly is observed in the upper part of the altered gabbro, while the lower part appears to be depleted in Ce. The similarity in the LREE-enriched fractionation patterns throughout the alteration profile suggests that the REE fractionation process is independent of the total REE content of the parent rock.